Connection rotation, a0

Connection rotation,

FIGURE 23.4 Three-parameter power model of semirigid connection.

Kishi and Chen [9] applied the model to four types of connections: single web-angle connections, double web-angle connections, top- and seat-angle connections, and top- and seat-angle with double web-angle connections. The detailed procedure to evaluate the three parameters Rki, Mu, and n for the four types of connections is described by Chen and Lui [10].

23.3.4 Four-Parameter Power Model

As experimental tests have shown that many semirigid connections do not exhibit the plateau in their M-d relationship shown in Figure 23.4 even at large rotation, the four-parameter power model shown in Equation 23.6 and Figure 23.5 has been adopted by a number of researchers [11-13] to simulate the nonlinear moment-rotation relationship of such connections:

where, as shown in Figure 23.5, R is the initial stiffness of the connection, Rp is the plastic stiffness of the connection, M0 is a reference moment, and n is a shape parameter. One of the advantages of this model is that it can easily represent simpler models, such as the linear model by setting Re = Rp and the three-parameter power model by setting Rp = 0. The model also approaches a bilinear model when n becomes large.

23.3.5 Connection Database

The connection database considered herein is a collection of experimental test results for different types of steel beam-to-column connections. The data usually collected are the corresponding details and dimensions of the connection, fastener, and connected beam and column. The purpose of the connection database is to provide the necessary information for the determination of the momentrotation characteristics of beam-to-column connections, which are often required by design standards in facilitating the analysis and design of semirigid framed structures.

As extensive tests had been previously conducted to investigate the moment-rotation characteristics of various types of connections, efforts to establish connection databases were initiated in 1980s. Goverhan [14] collected a total of 230 experimental moment-rotation curves and digitized them to form the corresponding database of connection behavior. Nethercot [15] conducted an extensive literature survey of more than 800 individual tests from over 70 studies. Kishi and Chen [16] expanded and extended Goverdhan's collection to a total 303 tests, which consisted of experimental data published from 1936 to 1985. After that, Kishi and his colleagues revised the database and appended 93 sets of experimental data published from 1986 to 1998.

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